Need Help to Improve Surface Finish

So the Z is jumping around and the sound of the X & Y steppers is different when cutting arcs or angles? What happens when you remove power from, say, the X driver (Y still powered up), and then reverse the situation? There seems to be some odd interaction going on between the axes.

Something else I would suggest would be to write up a table of each hypothesis, experiment and result. Or, since nothing has really solved the problem, at least a list of what you've tried and why. While you may think you've exhausted a particular avenue, you may find some holes in your testing while you are writing up your summary. This has been helpful for me when working on a gnarly problem.

Are you using the sense connections on your power supplies or are they unconnected?
 
homebrewed said:
So the Z is jumping around and the sound of the X & Y steppers is different when cutting arcs or angles? What happens when you remove power from, say, the X driver (Y still powered up), and then reverse the situation? There seems to be some odd interaction going on between the axes.

Something else I would suggest would be to write up a table of each hypothesis, experiment and result. Or, since nothing has really solved the problem, at least a list of what you've tried and why. While you may think you've exhausted a particular avenue, you may find some holes in your testing while you are writing up your summary. This has been helpful for me when working on a gnarly problem.

Are you using the sense connections on your power supplies or are they unconnected?
Click to expand...

Power supply sense connections? Here's a picture of the terminal connections on my X and Y power supplies.

Power Supply.jpg
 
spumco said:
I'm pretty stumped, too.

Shot in the dark here... Do you have one power supply for all three axis? I'm wondering - you mentioned motor noise changing - if the PS is acting wonky when there's a load from both X/Y at the same time. 'Cause you also mentioned that it's a problem on straight angle cuts, not just arcs, right? Any time you're cutting with both axis moving there's a problem?

Maybe a test doing an X/Z or Y/Z move might result in the same surface finish issue. Do a quickie CAD/CAM of a hill-shaped object and use a bullnose cutter with a parallel 3D contour.
Click to expand...


Today I ran a couple of tests in the XZ plane and the YZ plane. Below are pictures of each test done with a two flute 3/8" HSS ball end mill at 3000 rpm, .005" DOC and 010" stepover. As you can see there is virtually no difference in surface finish.

Grasping at straws, between the two tests, I ran a ground wire from my earth ground rod to my enclosure. Guess what? No change. Geez this is frustrating.

But I didn't come away empty handed. During the ZX test the motors emitted a monotone sound. Not so with the ZY test. The Y motor tone changed multiple times during each pass. There may be something there so tomorrow I'll pull the motor and check the ball nut mount and the ball screw AC bearings.

20170819_160953_resized.jpg


20170819_151107_resized.jpg
 
I think I found the problem, hopefully. I disassembled the Y axis ball screw bearing block and one of the AC bearings was in failure mode. Spinning it by hand it was rough. The other one was OK. I'm going to replace all four of the bearings on the X and Y axis while I have it apart. I'm praying this is it.
 
TomS said:
Power supply sense connections? Here's a picture of the terminal connections on my X and Y power supplies.

View attachment 240025
Click to expand...
Most high current PSU's have sense terminals, to compensate for voltage drops on the lines. I guess that's one of the things you give up with these types of inexpensive supplies. Or perhaps in this type of application there's not much benefit to be had (PWM stepper driver supply).

Good find with the rough bearing. Hopefully that's the source of your problem. Seems sort of strange for a bearing to go bad in that application. I'd double-check other components in the Y axis to make sure the bearing is not the result of some other problem. Otherwise you could be back in there sooner than you like.
 
homebrewed said:
Most high current PSU's have sense terminals, to compensate for voltage drops on the lines. I guess that's one of the things you give up with these types of inexpensive supplies. Or perhaps in this type of application there's not much benefit to be had (PWM stepper driver supply).

Good find with the rough bearing. Hopefully that's the source of your problem. Seems sort of strange for a bearing to go bad in that application. I'd double-check other components in the Y axis to make sure the bearing is not the result of some other problem. Otherwise you could be back in there sooner than you like.
Click to expand...

I've looked things over and didn't see anything else of concern. The ball nut mount is tight to the saddle and the ball screw rotated smoothly. I believe it's the bearings as they are cheap, as in poor quality, asian imports. They came with the bearing blocks. I've got four on order from VXB. Should be here on Wednesday.

Got my fingers crossed.
 
I hope that solves your problem but it would be an odd coincident that it would happen at the same time you changed the controller. I'll keep my fingers crossed for you.
 
jbolt said:
I hope that solves your problem but it would be an odd coincident that it would happen at the same time you changed the controller. I'll keep my fingers crossed for you.
Click to expand...

Looking back on some jobs prior to changing out the controller there were some surface finish issues starting to appear. They just were not bad enough at that time. Or I wasn't paying attention.

I'm hoping too!
 
You must log in or register to reply here.
Back
Top